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PostPosted: Thu Apr 16, 2009 5:20 am 
356 Fan
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Joined: Sun May 25, 2008 8:06 pm
Posts: 29
Location: London, UK
Dear Listers
I quick query about whether anyone is aware of the correct operating internal oil pressure of our 356 pushrod engines. I understand the relief valve opens at 18PSI and the maximum is regulated at 43PSI by the two internal relief valves.

I have a pressure gauge showing numerical pressure in Bar and my reading is between 2Bar (30PSI) at idle to 3Bar (43PSI) under hard acceleration in the pushrod engine. Under normal driving conditions with revs between 1,000rpm to 3,500rpm it is more between 2bar (30PSI) - 2.5bar (36PSI) is that your correct?

Thank you
John

356B T5 Roadster 1960
356 Carrera 2 GS 1964

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 Post subject: oil pressure
PostPosted: Thu Apr 16, 2009 7:56 am 
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Joined: Fri Dec 12, 2008 5:59 am
Posts: 203
John,
Yes I would say that is OK albeit slightly low. I've checked two C engines in the past and they would achieve maybe 0.5 bar higher than yours under similar conditions.
The manual states a max. of 3 bar when hot but does not mention rpm.
You could ask Barry Curtiss or Andy Prill for their opinion.

JF


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PostPosted: Thu Apr 16, 2009 8:35 am 
356 Fan
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Joined: Sun May 25, 2008 8:06 pm
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Location: London, UK
Just to add that I have a full flow hard line system with twin front coolers. I have a CPS pressure relief valve at the oil pump take-off however since it can still sends out high pressure out to the radiators in cold weather start-up I have installed in series an adjustable pressure relief valve which is great as I can control the pressure.

I have noticed that the more pressure relief I dial in, it corresponds to a reduction in internal oil pressure and noisy full flow start-up significantly reduce. With less pressure relief the internal pressure goes up and so does the oil pressure to the front cooler - which can go up to 8-10 bar when the engine is cold and the standard noisy full flow cold start-up is experienced. So I want to dial in the correct compromise adjustment to get the right range of internal pressure during normal engine revs ie 1,000rpm to 3,000rpm and not have high pressure to the front coolers. We know that all know that the maximum is 3 bar due to the engine's internal relief valve. But good to know that if the car is at say 1,000rpm what the PSI/Bar should be and at 2,000rpm what that should correspond to etc.

Thanking all 356 listers in advance!

My Best
John

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PostPosted: Thu Apr 16, 2009 9:01 am 
356 Fan

Joined: Thu Mar 27, 2008 1:04 pm
Posts: 98
John,
My SC has had an oil pressure gauge since new. I had a new sender and
the gauge calibrated in 2002 so it should be accurate, but it reads in
psi so you'll have to do the bar conversion. I get about 50 psi cold and
drops to just over 40 psi (probably the 43 psi relief setting) warm
above idle. This is with 15W40 Shell Rotella.
Dave Brenny
'64SC#219829

-----Original Message-----
From: John Heah [mailto:heahco@singnet.com.sg]
Sent: Thursday, April 16, 2009 4:20 AM
To: 356talk@356registry.com
Subject: [356Talk] Engine Internal Oil Pressure

Dear Listers
I quick query about whether anyone is aware of the correct operating
internal oil pressure of our 356 pushrod engines. I understand the
relief valve opens at 18PSI and the maximum is regulated at 43PSI by the
two internal relief valves.

I have a pressure gauge showing numerical pressure in Bar and my reading
is between 2Bar (30PSI) at idle to 3Bar (43PSI) under hard acceleration
in the pushrod engine. Under normal driving conditions with revs between
1,000rpm to 3,500rpm it is more between 2bar (30PSI) - 2.5bar (36PSI) is
that your correct?

Thank you
John

356B T5 Roadster 1960
356 Carrera 2 GS 1964

------------------------
John Heah




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 Post subject: oil pressure
PostPosted: Thu Apr 16, 2009 11:25 am 
356 Fan
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Joined: Fri Dec 12, 2008 5:59 am
Posts: 203
John,
I've looked at a few of these so-called up-graded systems and frankly they are crap. The relief valves are noisy and chatter because of poor design. Most of them are undersize for the job. Remember the pump will deliver 50/60 litres/min. at 5000 engine rpm so you must ask yourself where is all this oil going?

The noise reduces when you screw the valve down because you are stopping it relieving.
Without details of your plumbing it is difficult to explain why the bearing pressure drops - are you measuring it at the pressure switch?

If you see 10 bar on a gauge then that is over 3x the design load for the oil pump drive and that horrid little tang is enough of a problem with the std. set-up.

With the std. set-up the bi-pass valve ensures oil instantly gets to the bearings and it progressively closes and diverts more oil through the cooler to give a rapid warm-up. In hydraulic terms it is referred to as a hydrastat and it maintains a fixed pressure across the cooler. It's v.simple and v.clever really.

My advice is take it all that stuff off and just change the oil regularly.

JF


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PostPosted: Thu Apr 16, 2009 12:05 pm 
356 Fan
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Joined: Fri Dec 12, 2008 5:59 am
Posts: 203
Another thought for you John.
A likely explanation as to why the bearing pressure drops when you screw the R/V down is that the pump flow, at a given speed, will reduce because at a higher pressure the internal losses (slip) will increase. These pumps have quite generous clearances and the reduction in flow would be significant. So, although you may need a higher pressure to get the oil to the front coolers and back the net result is that the actual flow will be reduced leaving less oil to feed the bearings which are at the end of the line. Hence a lower pressure reading.

JF


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PostPosted: Thu Apr 16, 2009 12:38 pm 
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Joined: Sun May 25, 2008 8:06 pm
Posts: 29
Location: London, UK
Thanks for the responses. My set up is set up identical to a carrera down to the NOS Argus fittings and hardlines because a 4 cam is currently being rebuilt to take it's rightful place in the engine bay.

So the set up of the hardlines, argus connectors, braided hoses, oilstat and front coolers are per factory Carrera spec.

I agree the pressure relief at the oil pump outlet cover struggles to what it is designed to do. Assuming we can agree on the principle benefits of free flow setup, then a version with a pressure relief is better than one which does not have one. I know because I have witnessed how fast oil is expelled from a poor connection blow-out without a relief valve during a cold weather start. If you then agree that a relief valve at the outlet is better but insufficient capacity, then a larger secondary one along the oil lines is beneficial to do the remainder of the work. That is the basis of my set-up - assuming one agrees with free flow.

Of course if one does not agree with the principle and benefits of free flow then all this is purely academic. However when one does 2-3 hour runs on the auto-route/autobahns in Europe at 80mph-100mph before refueling and then the same again after topping up, the benefits of free flow with coolers gives one some comfort.

I appreciate in town driving or going on a gentle run along beautiful country side makes the set up an over kill.

My Best
John

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PostPosted: Thu Apr 16, 2009 11:35 pm 
John,
When I plumb a for a full flow filter system and/or aux.
coolers I do it from the a tap off from the front cover and
return it to the block. this can only be done while the
motor is apart to insure a clean install. The result is the
external system runs only what the motor regulates to
about 60-70 psi. It is mildly invasive since I believe in
welding in the AN fittings. The crankcase is too brittle to
just rely on NPT treads, it will crack at some time or get
loose. If you must go back to the original method they are
easy to cap off.

Alan

John Heah wrote:
Quote:
Just to add that I have a full flow hard line system with twin front
coolers. I have a CPS pressure relief valve at the oil pump take-off
however since it can still sends out high pressure out to the radiators
in cold weather start-up I have installed in series an adjustable
pressure relief valve which is great as I can control the pressure.

I have noticed that the more pressure relief I dial in, it corresponds
to a reduction in internal oil pressure and noisy full flow start-up
significantly reduce. With less pressure relief the internal pressure
goes up and so does the oil pressure to the front cooler - which can go
up to 8-10 bar when the engine is cold and the standard noisy full flow
cold start-up is experienced. So I want to dial in the correct
compromise adjustment to get the right range of internal pressure during
normal engine revs ie 1,000rpm to 3,000rpm and not have high pressure to
the front coolers. We know that all know that the maximum is 3 bar due
to the engine's internal relief valve. But good to know that if the car
is at say 1,000rpm what the PSI/Bar should be and at 2,000rpm what that
should correspond to etc.

Thanking all 356 listers in advance!

My Best
John


------------------------------------------------------------------------

John Heah




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